Pressure Control Valve

ABSTRACT

In a pressure controlling valve  3  for causing deformation of a resilient member  32  by a pressure difference between a CO 2  gas pressure in a sealed space (heat sensitive portion) corresponding to a refrigerant temperature and a high pressure of the CO 2  refrigerant in the refrigeration cycle to open and close the valve, a volume ratio Vs/(Vs−Vo) of a total volume (Vs) of the sealed space when the valve is fully closed and a total volume (Vo) of the sealed space when the valve is fully open is greater than 1.9 or 2.4. To improve this volume ratio, a cavity  31   d  communicating with the sealed space is formed inside a displacement transmission member  31  coupled with the resilient member, or a recess portion  35   a  is formed in a cover member  35   a , or a member communicating with the sealed space is connected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a pressure controlling valve (expansion valve) for controlling exit side pressure of a heat radiator (gas cooler) of a vapor compression system refrigeration cycle. More particularly, the invention is suitable for a supercritical refrigeration cycle using a refrigerant, such as carbon dioxide (CO₂) in a supercritical zone.

2. Description of the Related Art

In a refrigeration cycle using HFC134a as a refrigerant according to the prior art, a pressure controlling valve, such as the one disclosed in Japanese Unexamined Patent Publication No. 2002-13844 and shown in FIG. 14 has been used to control a degree of superheat of an evaporator exit refrigerant. This pressure controlling valve 3 includes a temperature sensitive portion 3 a, the internal pressure of which changes in accordance with a refrigerant temperature on the exit side of an evaporator 4, a film-like diaphragm 3 c partitioning the temperature sensitive portion 3 a from a space 3 b into which the refrigerant flowing out from the evaporator 4 is led and undergoes displacement in accordance with a pressure change inside the temperature sensitive portion 3 a, a throttle portion 3 d for reducing the pressure of the refrigerant, a valve body 3 e for adjusting an opening of the throttle portion 3 d and displacement transmission means 3 f for transmitting the displacement of the diaphragm 3 c to the valve body 3 e. A refrigerant passage 3 g for guiding refrigerant flowing out from the evaporator 4 to the side of diaphragm 3 c is provided to the displacement transmission means 3 f. Consequently, low temperature refrigerant flowing out from the evaporator 4 cools the diaphragm 3 c and even when the gas inside the temperature sensitive portion 3 a undergoes condensation and the condensed droplets absorb heat from external air and evaporate, the inside of the heat sensitive portion 3 a can be sufficiently cooled, thereby making it possible to prevent in advance the pressure inside the heat sensitive portion 3 a from elevating due to the influences of the ambient atmosphere around the heat sensitive portion.

In a refrigeration cycle using HFC134a for the refrigerant, the pressure controlling valve is used at a temperature below the critical temperature of the refrigerant to detect the temperature of the low pressure refrigerant, and the refrigerant sealed in a heat sensitive portion or sealed space at the upper part of the diaphragm, is used in a gas-liquid two-phase state. Since the refrigerant pressure in this gas-liquid two-phase state is solely determined by the temperature, the pressure controlling valve is always kept at a control pressure corresponding to a detection temperature even when the diaphragm undergoes displacement by the change of the refrigerant pressure in the refrigeration cycle, and consequently the volume of the sealed space (temperature sensitive portion) at the upper part of the diaphragm changes.

In a refrigeration cycle using carbon dioxide (CO₂) as the refrigerant, a supercritical condition is reached at a temperature higher than the critical temperature. Therefore, when the diaphragm undergoes displacement and the volume of the sealed space (temperature sensitive portion) at the upper part of the diaphragm changes, the pressure of the sealed refrigerant inside the sealed space changes in accordance with the volume change even at the same refrigerant temperature, and the control pressure of the pressure controlling valve also changes.

Therefore, in a refrigeration cycle using CO₂ refrigerant, a method of controlling high pressure at which a coefficient of performance (COP=Δi/ΔL: Δi is an enthalpy change quantity in the evaporation process, and ΔL is an enthalpy change quantity in the compression process) of the CO₂ cycle reaches a maximum with respect to the refrigerant temperature at the exit of the gas cooler (heat radiator) is known from Japanese Unexamined Patent Publication No. 9-264622. In the pressure controlling valve according to Japanese Unexamined Patent Publication No. 9-26422, the CO₂ refrigerant is sealed in the sealed space at the upper part of the diaphragm at a density ranging from a saturated solution density at a temperature of 0° C. to a saturated solution density at the critical point of the CO₂ refrigerant with respect to the sealed space volume in a state where the valve body closes the throttle portion. Consequently, the pressure on the exit side of the gas cooler and the exit side temperature of the gas cooler are controlled substantially along an optimal control line on the Mollier diagram and the CO₂ cycle can also be efficiently operated in the critical zone.

However, the pressure controlling valve according to Japanese Unexamined Patent Publication No. 9-264622 has the problem that when the change of the control pressure is greater than the diaphragm displacement, the control pressure greatly deviates from the high pressure (optimal pressure) at which COP (Coefficient of Performance) reaches a maximum, and COP drops.

When the elevation of the control pressure is greater than the diaphragm displacement, the pressure exceeds the maximum of the high pressure before the pressure controlling valve is fully open.

The pressure controlling valve for use in a refrigeration cycle using CO₂ refrigerant preferably exhibits a small drop of COP relative to the control pressure, but the sealed space (temperature sensitive portion) into which the gas is sealed must be increased in order to reduce the volume change of the pressure controlling valve relative to the valve opening. Accordingly, the pressure controlling valve becomes larger in size and production cost becomes higher.

In the refrigeration cycle using CO₂ refrigerant, the optimal high pressure (the pressure at which COP becomes maximal) also rises when the coolant temperature at the back of the gas cooler rises. When the high pressure becomes higher, there are problems that durability of the apparatus drops and the temperature of discharging the refrigerant becomes higher.

SUMMARY OF THE INVENTION

In view of the problems described above, it is an object of the present invention to provide a pressure controlling valve for use in a supercritical cycle, particularly in a refrigeration cycle using CO₂ for a refrigerant, that can restrain a control pressure from changing owing to displacement of a resilient member and can prevent an abnormal high pressure and drastic drop of COP (performance coefficient).

It is a second object of the invention to provide a pressure controlling valve capable of making small a sealed space (temperature sensitive portion) into which a gas is sealed, and holding down the increase of the size and production cost of the valve.

It is a third object of the invention to provide a pressure controlling valve capable of reducing a high pressure and preventing the drop of durability of an apparatus and rise of a discharge temperature.

In a pressure controlling valve for occurring to deform a resilient member 32 by a difference in pressure between a pressure of CO₂ gas in a sealed space A corresponding to a refrigerant temperature and highly pressurized CO₂ refrigerant in a refrigeration cycle and effecting opening and closing of a valve, one aspect of the present invention provides a pressure controlling valve wherein a volume ratio Vs/(Vs−Vo) of a total volume Vs of the sealed space when the valve is fully closed and a total volume Vo of the sealed space when the valve is fully open is at least 1.9. In this way, the sealed space (temperature sensitive portion) into which the CO₂ gas is sealed can be made compact, the change of the control pressure can be made small and the increase of the size and production cost of the pressure controlling valve can be reduced.

The pressure controlling valve according to the invention has a construction in which the volume ratio Vs/(Vs−Vo) is greater than a value of the volume ratio determined from FIG. 11 with respect to a CO₂ gas density in the sealed space when the valve is fully closed. In this case, the pressure controlling valve can make the sealed space small and can contribute to the decrease of the change of the control pressure.

A pressure controlling valve according to another aspect of the invention has a construction in which a volume ratio Vs/(Vs−Vo) of a total volume Vs of a sealed space when the valve is fully closed and a total volume Vo of the sealed space when the valve is fully open is at least 2.4. Consequently, it is possible to make a compact sealed space into which the CO₂ gas is sealed, thereby preventing the optimal high pressure from exceeding an upper limit value of 15 MPa and improving durability of an apparatus.

A pressure controlling valve according to another aspect of the invention has a construction in which a volume ratio Vs/(Vs−Vo) of a total volume Vs of a sealed space when the valve is fully closed and a total volume Vo of the sealed space when the valve is fully open is greater than a value determined from FIG. 12. Consequently, it is possible in this case to make a compact sealed space and prevent the optimal high pressure from exceeding the upper limit value.

A pressure controlling valve according to the invention has a construction in which control pressure is not greater than 14 MPa at a refrigerant temperature of 60° C. When the coolant temperature is 60° C., the high pressure is may exceed the upper limit value if the change of the control pressure is great. Therefore, the control pressure is set to 14 MPa or below.

A pressure controlling valve according to the invention has a construction in which control pressure is at least 9.5 MPa at a refrigerant temperature of 40° C. When the refrigerant temperature is 40C, the optimal high pressure is about 9.5 MPa and has a margin with respect to the upper limit value. Because the COP change with respect to the control pressure drastically drops at a pressure below the optimal high pressure, the control pressure is set to 9.5 MPa or more.

In the pressure controlling valve according to the invention, a space A₁ communicating with the sealed space is formed inside a displacement transmission member 31 hermetically coupled with the resilient member 32. Consequently, volume of the sealed space can be increased and the volume change with respect to the valve opening of the pressure controlling valve can be decreased. In other words, the change of the control pressure can be decreased.

In the pressure controlling valve according to the invention, opening and closing of the valve is effected by the displacement transmission member 31 coupled with the resilient member 32. In other words, opening and closing of the pressure controlling valve is executed by mechanical means.

In the pressure controlling valve according to the invention, a recess portion 35 a is formed in a cover member 35 on the side opposing the resilient member 32 relative to the sealed space A, or a member 7, 8 having a space communicating with the sealed space connected to the cover member 35. Accordingly, the volume of the sealed space can be increased and the volume change with respect to the valve opening of the pressure controlling valve can be decreased.

In the pressure controlling valve according to the invention, the resilient member 32 is a diaphragm or bellows.

The present invention will be understood more apparently from the description of the following preferred embodiments when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:

FIG. 1 is a schematic view of a refrigeration cycle having an internal heat exchanger and using a pressure controlling valve according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the pressure controlling valve of the first embodiment of the invention.

FIG. 3 is a schematic view of a refrigeration cycle using a pressure controlling valve according to a second embodiment of the present invention but not having an internal heat exchanger.

FIG. 4 is a sectional view of the pressure controlling valve of the second embodiment of the invention.

FIGS. 5A and 5B are a schematic view of a refrigeration cycle using a pressure controlling valve according to a third embodiment of the present invention but not having an internal heat exchanger and a schematic view of a refrigeration cycle using a pressure controlling valve according to a third embodiment of the present invention and having an internal heat exchanger.

FIG. 6 is a sectional view of the pressure controlling valve of the third embodiment of the invention.

FIG. 7 is a graph showing the relationship between a volume ratio of a sealed space of a pressure controlling valve at a refrigerant temperature of 40° C. and a change of quantity of control pressure when the pressure controlling valve changes from a full closure state to a full open state by using a density of the gas sealed in the sealed space as a parameter.

FIG. 8 is a graph showing the relationship between a volume ratio of a sealed space of a pressure controlling valve at a refrigerant temperature of 60° C. and a change quantity of a control pressure when the pressure controlling valve changes from a full closure state to a full open state by using a density of the gas sealed into the sealed space as a parameter.

FIG. 9 is a graph showing the relationship between a high pressure of a pressure controlling valve and COP in a refrigeration cycle having an internal heat exchanger by using a refrigerant temperature as a parameter.

FIG. 10 is a graph showing the relationship between a high pressure of a pressure controlling valve and COP in a refrigeration cycle not having an internal heat exchanger by using a refrigerant temperature as a parameter.

FIG. 11 is a graph showing a line of a control pressure change width 2 MPa at a refrigerant temperature of 40° C. by plotting a gas sealing density to the abscissa.

FIG. 12 is a graph showing a line of a control pressure change width 2 MPa at a refrigerant temperature of 60° C. by plotting a gas sealing density to the abscissa.

FIGS. 13A and 13B are explanatory views useful for explaining a valve closure state and a valve open state of a pressure controlling valve.

FIG. 14 is a sectional view of a pressure controlling valve according to the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pressure controlling valves according to embodiments of the present invention will be hereinafter explained with reference to the drawings. FIG. 1 is an explanatory view explaining a refrigeration cycle (supercritical refrigeration cycle) into which an internal heat exchanger is assembled, and which circulates CO₂ as a refrigerant. FIG. 2 shows a pressure controlling valve according to the first embodiment of the present invention that is applied to the refrigeration cycle shown in FIG. 1. In FIG. 1, reference numeral 1 denotes a compressor that sucks in and compresses a CO₂ refrigerant and reference numeral 2 denotes a gas cooler (heat radiator) that cools the refrigerant compressed by the compressor 1.

Reference numeral 3 denotes a pressure controlling valve (expansion valve) according to this embodiment. This pressure controlling valve 3 has a temperature sensitive portion (sealed space) A into which CO₂ gas is sealed, and controls refrigerant pressure on the exit side of the gas cooler 2 on the basis of the refrigerant temperature on the exit side of the gas cooler 2. Therefore, the pressure controlling valve operates also as a pressure reducing device that reduces the pressure of the high pressure refrigerant. The pressure controlling valve 3 has a valve function for opening and closing a refrigerant passage extending from the gas cooler 2 to the internal heat exchanger 6 and a refrigerant passage extending from the internal heat exchanger 6 to an evaporator 4. The pressure controlling valve 3 will be explained later in further detail.

The evaporator 4 evaporates a gas-liquid two-phase refrigerant the pressure of which is reduced by the pressure controlling valve 3, and cools air passing outside the evaporator 4. Reference numeral 5 denotes an accumulator that separates the gaseous refrigerant from the liquid phase refrigerant and temporarily stores excess refrigerant inside the refrigeration cycle. Reference numeral 6 denotes the internal heat exchanger that is arranged inside the refrigeration cycle so that refrigerant that flows from the gas cooler 2 to the pressure controlling valve 3 and the refrigerant flowing from the accumulator 5 to the compressor 1 conduct heat-exchange with each other. The compressor 1, the gas cooler 2, the pressure controlling valve 3, the evaporator 4, the accumulator 5 and the internal heat exchanger 6 are connected to one another through piping and constitute a closed circuit. Therefore, CO₂ refrigerant discharged from the compressor 1 is taken into the original compressor 1 through the gas cooler 2→internal heat exchanger 6→pressure controlling valve 3→evaporator 4→accumulator 5→internal heat exchanger 6.

Next, the pressure controlling valve 3A of the first embodiment used for the refrigeration cycle shown in FIG. 1 will be explained with reference to FIG. 2. A first flow passage F1 as a part of the refrigerant flow passage extending from the gas cooler 2 to the internal heat exchanger 6 and a second flow passage F2 as a part of the refrigerant flow passage extending from the internal heat exchanger 6 to the evaporator 4 through a valve port 33 g are independently formed inside a body 33 of the pressure controlling valve 3A. To install the pressure sensitive portion (sealed space) later described, a first opening 33 e is arranged on the heat sensitive portion and a second opening 33 f for setting an adjustment spring 36 is arranged at a lower part besides an inflow port 33 a connected to the gas cooler (2) side and an outflow port 33 b connected to the internal hat exchanger side that together constitute the first flow passage F1 and an inflow port 33 c connected to the internal heat exchanger (6) side and an outflow port 33 d connected to the evaporator (4) side that together constitute the second flow passage F2.

A displacement transmission member 31 having a valve portion 31 a formed at its distal end is accommodated in the body 33 and the valve portion 31 a of the displacement transmission member 31 opens and closes a valve port 33 g. Consequently, the second flow passage F2 is opened and closed and the internal heat exchanger 6 and the evaporator 4 are communicated with, and cut off from, each other.

A temperature sensitive portion is fitted to a first opening 33 e of the body 33. The temperature sensitive portion includes a resilient member 32, such as a diaphragm or bellows, a cover member 35, a lower support member 34, and a sealed space A is formed inside the temperature sensitive portion. In other words, a recess 35 a for forming the sealed space A is formed at the center of the cover member 35 and the peripheral edge of the resilient member 32 is clamped and fixed by the cover material 35 and the lower support member 34 to form the temperature sensitive portion. The resilient member 32 has a thin film made of stainless steel and undergoes deformation and displacement in accordance with the pressure difference between the inside and the outside of the sealed space A. The lower support member 34 has a cylindrical portion 34 a and a flange portion 34 b, and a screw portion formed around the outer circumference of the cylindrical portion 34 a is mated with the first opening 33 e of the body 33, thereby fixing the temperature sensitive portion to the body 33. A filling pipe 35 b is fitted to the cover member 35 and a gas, such as CO₂ is sealed from the filling pipe 35 b into the sealed space A. The filling pipe 35 b is closed after the gas is sealed.

One of the end portions 31 b of the displacement transmission member 31 that extends upward from the valve portion 31 a through the cylindrical portion 34 a of the lower support member 34 is fixed to the resilient member 32 and a clearance B having an annular sectional shape is defined between the inner surface of the cylindrical portion 34 a and the outer peripheral surface of the displacement transmission member 31. This clearance B communicates with the first flow passage F1 connected to the exit side of the gas cooler 2. As a result, the refrigerant on the exit side of the gas cooler 2 flows into the clearance B and the refrigerant temperature is transmitted to the gas inside the sealed space A. At the same time, the pressure of the refrigerant on the exit side of the gas cooler 2 operates on the resilient member 32.

A cavity (space A₁) 31 d communicating with the sealed space A of the temperature sensitive portion is formed at an end portion 31 b of the displacement transmission member 31. To communicate the cavity 31 d with the sealed space A in this case, a through-hole 32 a is naturally formed in the resilient member 32, and the sealed space A and the cavity (space A₁) 31 d communicate with each other through this through-hole 32 a. According to this construction, the sealed space of the temperature sensitive portion can be set to the sum of the sealed space A+space A₁ and the sealed space can be expanded, so that accuracy of the temperature sensitive portion can be improved.

An adjustment nut 37 meshes with the other end portion 31 c of the displacement transmission member 31 extending downward below the valve portion 31 a through the valve port 33 g. An adjustment spring 36 for forcing the valve portion 31 a of the displacement transmission member 31 in the closing direction of the valve is interposed between the lower surface of the valve port 33 g and the adjustment nut 37. An initial set load of the adjustment spring 36 (elastic force under the closure state of the valve port 33 g) can be arbitrarily adjusted by turning the adjustment nut 37. The adjustment spring 36, adjustment nut 37, and so forth, are disposed inside a downstream space 37 as a part of the second flow passage F2 connected to the entry side of the evaporator 4. When the cap 38 is fitted into the second opening 33 f of the body 33, the lower part of the downstream space C is closed.

In the pressure controlling valve 3A of the first embodiment having the construction described above, the valve closing force of the displacement transmission member 31 is acquired by the internal pressure inside the sealed space (A+A₁) and the adjustment spring 36, and the valve opening force of the displacement transmission member 31 is acquired by the refrigerant pressure on the exist side of the gas cooler 2. The pressure controlling valve 3A is opened and closed in accordance with the balance of both of the valve opening and closing forces. The internal pressure of the sealed space (A+A₁) changes depending on the refrigerant temperature on the exit side of the gas cooler 2 flowing into the clearance B, and as the opening of the valve port 33 g thus changes, the refrigerant pressure on the exist side of the internal heat exchanger 6 is controlled.

It is known that in a refrigeration cycle using CO₂ as the refrigerant, there is high pressure at which COP (performance coefficient) reaches a maximum. The use of an internal heat exchanger 6 for effecting heat exchange between the refrigerant at the exit of the gas cooler 2 and the taken-in refrigerant of the compressor 1 has been proposed as a means for improving COP.

FIG. 9 is a graph showing the relationship between the high pressure and COP by plotting the cases of the outlet refrigerant temperature of 40° C., 50° C. and 60° C. when the internal heat exchanger 6 is used, the temperature of the evaporator 4 is 20° C. and the superheat quantity (the degree of superheat) of the taken-in refrigerant of the compressor 1 is 20° C., respectively.

The pressure controlling valve 3 (3A) used for the cycle of the CO₂ refrigerant regulates the high pressure of the cycle to the pressure at which COP becomes maximal with respect to the exit refrigerant temperature of the gas cooler 2. Therefore, the pressure controlling characteristics are regulated by the sealed gas density, etc, of the heat sensitive portion (sealed space) of the pressure controlling valve 3 (3A) so as to achieve the temperature-pressure characteristics indicated by a dashed line in FIG. 9.

The CO₂ gas or a mixture of the CO₂ gas and a small amount of an inert gas, such as nitrogen gas is sealed into the temperature sensitive portion (sealed space) of the pressure controlling valve 3 (3A). Since the CO₂ gas reaches a supercritical state at a temperature of about 31° C. or above, the volume of the sealed space A or (A+A₁) into which the gas is sealed changes, with the displacement of the resilient member 32, such as the diaphragm or the bellows, so that the pressure inside the sealed space changes even though the exit refrigerant temperature of the gas cooler 2 does not change.

The pressure controlling valve 3 opens and closes the valve in accordance with the displacement of the resilient member 32. Therefore, when the valve is open as shown in FIG. 13A, the resilient member 32 deforms to a convex state in the down direction, but when the flow rate of the refrigerant increases and the valve lift quantity becomes great, the resilient member 32 undergoes displacement upward and the volume of the sealed space of the temperature sensitive portion becomes small. The sealing density of the gas increases and the pressure rises, too. Consequently, the control pressure increases when the opening of the pressure controlling valve 3 increases as shown in FIG. 13B.

The drop of COP relative to the control pressure is preferably as small as possible. To reduce the volume change with respect to the valve opening of the pressure controlling valve 3, the sealed space into which the gas is sealed must be increased. In this embodiment, therefore, the sealed spaces A, A+A₁ are increased by forming the recess portion 35 a on the cover member 35 and/or forming the cavity portion 31 d in the displacement transmission member 31.

FIGS. 7 and 8 represent the degree of the change of the control pressure when the valve changes from the full closure state to full open state with respect to the volume ratio of the sealed space at the refrigerant temperatures of 40° C. and 60° C., respectively, by using the sealed gas density as a parameter.

The volume ratio is defined by Vs/(Vs−Vo) where Vs is the total volume of the sealed space at the time of closing of the valve and Vo is the total volume of the sealed space at the time of opening of the valve.

In other words, the volume ratio represents how many times of volume (Vs) of the volume change quantity (Vs−Vo) owing to opening/closing of the valve is necessary relative to the change of the control pressure.

FIG. 7 shows the necessary volume ratio at a refrigerant temperature of 40° C. The volume ratio rapidly increases from a pressure change of not greater than 1 MPa at a relatively low sealing density (300 kg/m³) used as the pressure controlling valve 3 though the value changes dependent on the sealed gas density. In the case of a relatively high sealing density (600 kg/m³), on the other hand, the volume ratio rapidly increases from the pressure change of below 2 MPa and the necessary volume of the sealed space becomes great. Incidentally, the sealing density represents the density with respect to the volume of the sealed space at the closure of the valve.

Similarly, at a refrigerant temperature of 60° C. as shown in FIG. 8, the volume ratio rapidly increases from below 2 MPa in the case of the sealing density of 300 kg/m³, and rapidly increases from below 4 MPa in the case of the sealing density of 600 kg/m³, and the necessary volume of the sealed becomes great.

It can be understood from above that in order to make the temperature sensitive portion of the pressure controlling valve 3 compact, the change of the control pressure is preferably 1 to 2 MPa when the refrigerant temperature is 40° C. and 2 to 4 MPa at the refrigerant temperature of 60° C.

Next, the COP change of the cycle with respect to the control pressure will be explained as shown in FIG. 9. The pressure change width at the COP drop ratio of 10% is 3 MPa at the refrigerant temperature of 40° C., 4.2 MPa at the refrigerant temperature of 50° C. and 6.7 MPa at the refrigerant temperature of 60° C. The same COP drop ratio is scored with a pressure change width of at least twice at the refrigerant temperatures of 50° C. and 60° C. with respect to the pressure change width at the refrigerant temperature of 40° C.

When the volume ratio is constant, the change width of the control pressure at the refrigerant temperature of 60° C. is about twice the change width at a refrigerant temperature of 40° C., but an equal level of the COP drop ratio of the cycle can be obtained.

FIG. 10 shows the COP change of the cycle with respect to the control pressure when the internal heat exchanger 6 is not used. Because the pressure change width at the same COP drop ratio is greater than when the internal heat exchanger 6 shown in FIG. 9 is used, COP does not greatly drop even when the pressure controlling valve 3 of this embodiment is used in the case where the internal heat exchanger 6 is not used.

FIG. 11 is a graph showing the relationship between the volume ratio of the sealed space at the refrigerant temperature of 40° C. in FIG. 7 and the change quantity of the control pressure when the valve changes from the full closure to the full open state with the sealed gas density as a parameter. The abscissa represents the sealing density and the ordinate does the volume ratio. The graph shows the line of the control pressure change width 2 MPa at the refrigerant temperature of 40° C.

It can be understood from above that in order to make small the temperature sensitive portion (sealed space) of the pressure controlling valve 3 and to minimize the change of the control pressure, it is necessary to employ the following measures:

(1) at least the volume ratio is set to 1.9 or more (at the gas sealing density of 300 kg/m³); and

(2) the volume ratio is made greater than the solid line in FIG. 11 with respect to the gas sealing density.

In the refrigeration cycle of the CO₂ refrigerant, the optimal high pressure (the pressure at which COP becomes maximal) rises, too, when the refrigerant temperature at the exit of the gas cooler 2 rises. When the high pressure becomes higher, however, the problems occur in that durability of the apparatus drops and the discharge temperature of the compressor 1 rises. For this reason, a pressure of about 15 MPa is set in many cases as the upper limit value of the high pressure.

When the internal heat exchanger 6 is used as shown in FIG. 9, the optimal high pressure is about 14 MPa when the refrigerant temperature is 60° C. and often exceeds the upper limit value of 15 MPa if the change of the control pressure is large.

The COP change with respect to the control pressure is small when the refrigerant temperature is 60° C. as shown in FIG. 9. When the lower limit value of the control pressure is set to 12 MPa, therefore, a margin width of about 3 MPa can be acquired with respect to the upper limit value.

FIG. 12 is a graph showing the relation between the volume ratio of the sealed space at the refrigerant temperature of 60° C. in FIG. 8 and the change quantity of the control pressure when the valve changes from the full closure to the full open with the sealed gas density as a parameter. The abscissa represents the sealing density and the ordinate does the volume ratio. The graph shows the line of the control pressure change width 3 MPa at the refrigerant temperature of 60° C.

It can be understood that to make small the sealed space as the gas sealing portion of the pressure controlling valve 3 and to prevent the control pressure from exceeding the upper limit value (15 MPa), the following may well be employed:

(1) at least the volume ratio is set to 2.4 or more (at the gas sealing density of 300 kg/m³); or

(2) the volume ratio is made greater than the solid line in FIG. 12 with respect to the gas sealing density; and

(3) the pressure at which the pressure controlling valve opens is set to a pressure lower than the optimal high pressure (14 MPa).

The optimal high pressure is about 9.5 MPa at the refrigerant temperature of 40° C. and has a margin to the upper limit pressure. Since the COP change with respect to the control pressure drastically drops below the optimal high pressure, a large COP change can be prevented even when the control pressure exhibits some variance when the pressure at the opening of the pressure controlling valve 3 is the optimal high pressure.

FIG. 3 is an explanatory view useful for explaining the refrigeration cycle of the CO₂ refrigerant without incorporating the internal heat exchanger. FIG. 4 shows a pressure controlling valve 3B according to the second embodiment of the invention that is applied to the refrigeration cycle shown in FIG. 3. The same reference numeral is used to identify the same constituent member as in FIG. 1. In other words, reference numeral 1 denotes the compressor for sucking and compressing the CO₂ refrigerant. Reference numeral 2 denotes the gas cooler for cooling the refrigerant compressed by the compressor 1. The pressure controlling valve 3 (3B) for controlling the refrigerant pressure on the exit side of the gas cooler 2 on the basis of the refrigerant temperature on the exit side of the gas cooler 2 is arranged on the exit side of the gas cooler 2 and operates as a pressure reducing device for reducing the pressure of the high pressure refrigerant.

Reference numeral 4 denotes the evaporator for evaporating the gas-liquid two-phase refrigerant the pressure of which is reduced by the pressure controlling valve 3. Reference numeral 5 denotes the accumulator for separating the gaseous phase refrigerant from the liquid phase refrigerant and temporarily storing the excess refrigerant inside the refrigeration cycle. The compressor 1, the gas cooler 2, the pressure controlling valve 3, the evaporator 4 and the accumulator 5 are connected to one another through piping and form a closed circuit.

The pressure controlling valve 3B according to the second embodiment of the invention and shown in FIG. 3 is used in the cycle not using the internal heat exchanger. Therefore, only a flow passage F as a part of the refrigerant flow passage extending from the gas cooler 2 to the evaporator 4 through the valve port 33 g is formed inside the body 33 of the pressure controlling valve 3B. The second opening 33 f of the body 33 of the pressure controlling valve 3B is closed, and the extension portion below the valve portion 31 a of the displacement transmission member 31, the adjustment spring 36 and the adjustment nut 37 are omitted. Furthermore, the cavity 31 d formed at one of the ends 31 b of the displacement transmission member 31 is omitted. Accordingly, the sealed space A is formed by the recess portion 35 a disposed in the cover member 35. The rest of the constructions are the same as those of the first embodiment and the explanation will be omitted.

Only the internal pressure by the gas sealed into the sealed space A, into which the refrigerant temperature on the exit side of the gas cooler 2 flowing into the clearance B is transmitted, operates as the valve closing force of the displacement transmission member 31 in the second embodiment, and the refrigerant pressure on the exit side of the gas cooler 2 operates as the valve opening force. In this case, the gas sealed into the sealed space A also performs the function of the adjustment spring 36. Here, the CO₂ gas that changes the internal pressure in accordance with the temperature and a small amount of an inert gas, such as a nitrogen gas that generates an internal pressure of a substantially constant level without changing the internal pressure in accordance with the temperature within the temperature range of the detection object are mixed and sealed.

In the second embodiment, the recess portion 35 a of the cover member 35 of the resilient member 32 is made as large as possible to secure the volume ratio by increasing the volume of the sealed space A as the temperature sensitive portion.

FIGS. 5A and 5B are schematic views of the refrigeration cycles of the CO₂ refrigerant in the case where the pressure controlling valve 3C according to the third embodiment is used, but the internal heat exchanger 6 is not used and in the case where the internal heat exchanger 6 is used, respectively. FIG. 6 shows the pressure controlling valve 3C according to the third embodiment of the invention. The arrangement of the constituent elements in the schematic view of the refrigeration cycle shown in FIG. 5A is basically the same as that of the refrigeration cycle shown in FIG. 3 with the exception of the construction of the pressure controlling valve 3. The schematic view of the refrigeration cycle in FIG. 5B is basically the same as the refrigeration cycle shown in FIG. 1 and the explanation will be therefore omitted. In other words, the pressure controlling valve 3 shown in FIGS. 5A and 5B has a capillary tube 7 connected to the sealed space A as the heat sensitive portion and a temperature sensitive cylinder 8 arranged at the distal end of the capillary tube 7. This temperature sensitive cylinder 8 is disposed to keep contact with the exit piping of the gas cooler 2.

In the pressure controlling valve 3C according to the third embodiment of the present invention, only one flow passage F is formed inside the body 33. This flow passage F is used as a part of the refrigerant flow passage extending from the gas cooler 2 to the evaporator 4 through the valve port 33 g when the pressure controlling valve 3C is used for the cycle not having the internal heat exchanger 6 shown in FIG. 5A and when used for the cycle using the internal heat exchanger 6 shown in FIG. 5B, the flow passage F is used as a part of the refrigerant flow passage extending from the internal heat exchanger 6 to the evaporator 4 through the valve port 33 g. The cavity 31 d is not formed at one of the ends of the displacement transmission member 31. Instead, the capillary tube 7 having the temperature sensitive cylinder 8 at its distal end is fitted as a member communication with the sealed space A to the cover member 35 and the inside of the capillary tube 7 is connected with the sealed space A. Therefore, the volume of the sealed space into which the gas is sealed can be increased. The rest of the constructions are the same as those of the pressure controlling valve 3A of the first embodiment.

In the pressure controlling valve 3C according to this third embodiment, the valve closing force and the valve opening force of the displacement transmission member 31 operates in the same way as those of the pressure controlling valve 3A of the first embodiment, but the sealed gas inside the sealed space mainly receives the thermal influences from the heat sensitive cylinder 8 arranged at the exit piping of the gas cooler 2.

Incidentally, the present invention has been described in detail on the basis of the specific embodiments thereof, but can be changed or modified in various ways by those skilled in the art without departing from the scope and spirit of the invention. 

1. A pressure controlling valve for use in a refrigeration cycle using a CO₂ refrigerant, for generating pressure corresponding to a refrigerant temperature by transferring heat of the refrigerant to a CO₂ gas sealed in a sealed space (A), and causing deformation of a resilient member by a pressure difference between a gas pressure in said sealed space and a high pressure of said refrigerant in said refrigeration cycle to open and close said valve, wherein a volume ratio Vs/(Vs−Vo) of a total volume (Vs) of said sealed space when said valve is fully closed and a total volume (Vo) of said sealed space when said valve is fully open satisfies the following relation: Vs/(Vs−Vo)≧1.9.
 2. A pressure controlling valve as defined in claim 1, wherein said volume ratio Vs/(Vs−Vo) is greater than a value of said volume ratio determined from FIG. 11 with respect to a CO₂ gas density in said sealed space when said valve is fully closed.
 3. A pressure controlling valve as defined in claim 1, wherein a control pressure of said pressure controlling valve is not greater than 14 MPa at a refrigerant temperature of 60° C.
 4. A pressure controlling valve as defined in claim 1, wherein a control pressure of said pressure controlling valve is at least 9.5 MPa at a refrigerant temperature of 40° C.
 5. A pressure controlling valve as defined in claim 1, wherein a space (A1) communicating with said sealed space is formed inside a displacement transmission member hermetically coupled with said resilient member.
 6. A pressure controlling valve as defined in claim 5, wherein opening/closing of said valve is made by said displacement transmission member coupled with said resilient member.
 7. A pressure controlling valve as defined in claim 1, wherein a recess portion is formed in a cover member on the side opposing said resilient member relative to said sealed space, or a member having a space communicating with said sealed space is connected to said cover member.
 8. A pressure controlling valve as defined in claim 1, wherein said resilient member is a diaphragm or bellows.
 9. A pressure controlling valve for use in a refrigeration cycle using a CO₂ refrigerant, for generating a pressure corresponding to a refrigerant temperature by transferring heat of the refrigerant to a CO₂ gas sealed in a sealed space (A), and causing deformation of a resilient member by a pressure difference between a gas pressure in said sealed space and a high pressure of said refrigerant in said refrigeration cycle to open and close said valve, wherein a volume ratio Vs/(Vs−Vo) of a total volume (Vs) of said sealed space when said valve is fully closed and a total volume (Vo) of said sealed space when said valve is fully open satisfies the following relation: Vs/(Vs−Vo)≧2.4.
 10. A pressure controlling valve as defined in claim 9, wherein said volume ratio Vs/(Vs−Vo) is greater than a value of said volume ratio determined from FIG. 12 with respect to a CO₂ gas density in said sealed space when said valve is fully closed.
 11. A pressure controlling valve as defined in claim 9, wherein a control pressure of said pressure controlling valve is not greater than 14 MPa at a refrigerant temperature of 60° C.
 12. A pressure controlling valve as defined in claim 9, wherein a control pressure of said pressure controlling valve is at least 9.5 MPa at a refrigerant temperature of 40° C.
 13. A pressure controlling valve as defined in claim 9, wherein a space (A1) communicating with said sealed space is formed inside a displacement transmission member hermetically coupled with said resilient member.
 14. A pressure controlling valve as defined in claim 9, wherein opening/closing of said valve is made by said displacement transmission member coupled with said resilient member.
 15. A pressure controlling valve as defined in claim 9, wherein a recess portion is formed in a cover member on the side opposing said resilient member relative to said sealed space, or a member having a space communicating with said sealed space is connected to said cover member.
 16. A pressure controlling valve as defined in claim 9, wherein said resilient member is a diaphragm or bellows. 